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Date: Mon, 13 Dec 2021 10:06:01 +0000
From: Mark Rutland <mark.rutland@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: will@...nel.org, boqun.feng@...il.com,
linux-kernel@...r.kernel.org, x86@...nel.org, elver@...gle.com,
keescook@...omium.org, hch@...radead.org,
torvalds@...ux-foundation.org, axboe@...nel.dk
Subject: Re: [PATCH v2 3/9] atomic: Introduce
atomic_{inc,dec,dec_and_test}_overflow()
On Fri, Dec 10, 2021 at 05:16:21PM +0100, Peter Zijlstra wrote:
> In order to facilitate architecture support for refcount_t, introduce
> a number of new atomic primitives that have a uaccess style exception
> for overflow.
>
> Notably:
>
> atomic_inc_overflow(v, Label):
>
> increment and goto Label when the old value of v is zero or
> negative.
>
> atomic_dec_overflow(v, Label):
>
> decrement and goto Label when the new value of v is zero or
> negative
>
> atomic_dec_and_test_overflow(v, Label):
>
> decrement and return true when the result is zero and goto
> Label when the new value of v is negative
Maybe it's worth adding these as comments in the fallback, which we have for a
few existing functions, e.g.
| /**
| * arch_${atomic}_add_negative - add and test if negative
| * @i: integer value to add
| * @v: pointer of type ${atomic}_t
| *
| * Atomically adds @i to @v and returns true
| * if the result is negative, or false when
| * result is greater than or equal to zero.
| */
| static __always_inline bool
| arch_${atomic}_add_negative(${int} i, ${atomic}_t *v)
| {
| return arch_${atomic}_add_return(i, v) < 0;
| }
Not a big deal either way.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> include/linux/atomic/atomic-arch-fallback.h | 64 ++++++++++++++++++++++++
> include/linux/atomic/atomic-instrumented.h | 65 ++++++++++++++++++++++++-
> include/linux/atomic/atomic-long.h | 32 +++++++++++-
> scripts/atomic/atomics.tbl | 3 +
> scripts/atomic/fallbacks/dec_and_test_overflow | 12 ++++
> scripts/atomic/fallbacks/dec_overflow | 8 +++
> scripts/atomic/fallbacks/inc_overflow | 8 +++
> 7 files changed, 189 insertions(+), 3 deletions(-)
>
> --- a/include/linux/atomic/atomic-arch-fallback.h
> +++ b/include/linux/atomic/atomic-arch-fallback.h
> @@ -1250,6 +1250,37 @@ arch_atomic_dec_if_positive(atomic_t *v)
> #define arch_atomic_dec_if_positive arch_atomic_dec_if_positive
> #endif
>
> +#ifndef arch_atomic_inc_overflow
> +#define arch_atomic_inc_overflow(_v, _label) \
> +do { \
> + int __old = arch_atomic_fetch_inc(_v); \
> + if (unlikely(__old <= 0)) \
> + goto _label; \
> +} while (0)
> +#endif
> +
> +#ifndef arch_atomic_dec_overflow
> +#define arch_atomic_dec_overflow(_v, _label) \
> +do { \
> + int __new = arch_atomic_dec_return(_v); \
> + if (unlikely(__new <= 0)) \
> + goto _label; \
> +} while (0)
> +#endif
> +
> +#ifndef arch_atomic_dec_and_test_overflow
> +#define arch_atomic_dec_and_test_overflow(_v, _label) \
> +({ \
> + bool __ret = false; \
> + int __new = arch_atomic_dec_return(_v); \
> + if (unlikely(__new < 0)) \
> + goto _label; \
> + if (unlikely(__new == 0)) \
> + __ret = true; \
> + __ret; \
> +})
> +#endif
I had wanted to move at least part of this to a function to ensure
single-evaluation and avoid accidental symbol aliasing, but (as we discussed
over IRC) I couldn't find any good way to do so, and given this is sufficiently
specialise I think we should be ok with this as-is. It's certainly no worse
than the existing stuff for xchg/cmpxchg.
With that in mind, these (and the other variants, and the underlying fallback
templates) all look good to me.
With or without the comments as above:
Reviewed-by: Mark Rutland <mark.rutland@....com>
Mark.
> +
> #ifdef CONFIG_GENERIC_ATOMIC64
> #include <asm-generic/atomic64.h>
> #endif
> @@ -2357,5 +2388,36 @@ arch_atomic64_dec_if_positive(atomic64_t
> #define arch_atomic64_dec_if_positive arch_atomic64_dec_if_positive
> #endif
>
> +#ifndef arch_atomic64_inc_overflow
> +#define arch_atomic64_inc_overflow(_v, _label) \
> +do { \
> + s64 __old = arch_atomic64_fetch_inc(_v); \
> + if (unlikely(__old <= 0)) \
> + goto _label; \
> +} while (0)
> +#endif
> +
> +#ifndef arch_atomic64_dec_overflow
> +#define arch_atomic64_dec_overflow(_v, _label) \
> +do { \
> + s64 __new = arch_atomic64_dec_return(_v); \
> + if (unlikely(__new <= 0)) \
> + goto _label; \
> +} while (0)
> +#endif
> +
> +#ifndef arch_atomic64_dec_and_test_overflow
> +#define arch_atomic64_dec_and_test_overflow(_v, _label) \
> +({ \
> + bool __ret = false; \
> + s64 __new = arch_atomic64_dec_return(_v); \
> + if (unlikely(__new < 0)) \
> + goto _label; \
> + if (unlikely(__new == 0)) \
> + __ret = true; \
> + __ret; \
> +})
> +#endif
> +
> #endif /* _LINUX_ATOMIC_FALLBACK_H */
> -// cca554917d7ea73d5e3e7397dd70c484cad9b2c4
> +// e4c677b23b3fd5e8dc4bce9d6c055103666cfc4a
> --- a/include/linux/atomic/atomic-instrumented.h
> +++ b/include/linux/atomic/atomic-instrumented.h
> @@ -599,6 +599,27 @@ atomic_dec_if_positive(atomic_t *v)
> return arch_atomic_dec_if_positive(v);
> }
>
> +#define atomic_inc_overflow(v, L) \
> +({ \
> + typeof(v) __ai_v = (v); \
> + instrument_atomic_read_write(__ai_v, sizeof(*__ai_v)); \
> + arch_atomic_inc_overflow(__ai_v, L); \
> +})
> +
> +#define atomic_dec_overflow(v, L) \
> +({ \
> + typeof(v) __ai_v = (v); \
> + instrument_atomic_read_write(__ai_v, sizeof(*__ai_v)); \
> + arch_atomic_dec_overflow(__ai_v, L); \
> +})
> +
> +#define atomic_dec_and_test_overflow(v, L) \
> +({ \
> + typeof(v) __ai_v = (v); \
> + instrument_atomic_read_write(__ai_v, sizeof(*__ai_v)); \
> + arch_atomic_dec_and_test_overflow(__ai_v, L); \
> +})
> +
> static __always_inline s64
> atomic64_read(const atomic64_t *v)
> {
> @@ -1177,6 +1198,27 @@ atomic64_dec_if_positive(atomic64_t *v)
> return arch_atomic64_dec_if_positive(v);
> }
>
> +#define atomic64_inc_overflow(v, L) \
> +({ \
> + typeof(v) __ai_v = (v); \
> + instrument_atomic_read_write(__ai_v, sizeof(*__ai_v)); \
> + arch_atomic64_inc_overflow(__ai_v, L); \
> +})
> +
> +#define atomic64_dec_overflow(v, L) \
> +({ \
> + typeof(v) __ai_v = (v); \
> + instrument_atomic_read_write(__ai_v, sizeof(*__ai_v)); \
> + arch_atomic64_dec_overflow(__ai_v, L); \
> +})
> +
> +#define atomic64_dec_and_test_overflow(v, L) \
> +({ \
> + typeof(v) __ai_v = (v); \
> + instrument_atomic_read_write(__ai_v, sizeof(*__ai_v)); \
> + arch_atomic64_dec_and_test_overflow(__ai_v, L); \
> +})
> +
> static __always_inline long
> atomic_long_read(const atomic_long_t *v)
> {
> @@ -1755,6 +1797,27 @@ atomic_long_dec_if_positive(atomic_long_
> return arch_atomic_long_dec_if_positive(v);
> }
>
> +#define atomic_long_inc_overflow(v, L) \
> +({ \
> + typeof(v) __ai_v = (v); \
> + instrument_atomic_read_write(__ai_v, sizeof(*__ai_v)); \
> + arch_atomic_long_inc_overflow(__ai_v, L); \
> +})
> +
> +#define atomic_long_dec_overflow(v, L) \
> +({ \
> + typeof(v) __ai_v = (v); \
> + instrument_atomic_read_write(__ai_v, sizeof(*__ai_v)); \
> + arch_atomic_long_dec_overflow(__ai_v, L); \
> +})
> +
> +#define atomic_long_dec_and_test_overflow(v, L) \
> +({ \
> + typeof(v) __ai_v = (v); \
> + instrument_atomic_read_write(__ai_v, sizeof(*__ai_v)); \
> + arch_atomic_long_dec_and_test_overflow(__ai_v, L); \
> +})
> +
> #define xchg(ptr, ...) \
> ({ \
> typeof(ptr) __ai_ptr = (ptr); \
> @@ -1912,4 +1975,4 @@ atomic_long_dec_if_positive(atomic_long_
>
>
> #endif /* _LINUX_ATOMIC_INSTRUMENTED_H */
> -// 66cdf9a0e0a995cba29c61baf018f7ef35974ae5
> +// 702806891ef1d01d76767c55088264ab6a1ef77d
> --- a/include/linux/atomic/atomic-long.h
> +++ b/include/linux/atomic/atomic-long.h
> @@ -515,6 +515,21 @@ arch_atomic_long_dec_if_positive(atomic_
> return arch_atomic64_dec_if_positive(v);
> }
>
> +#define arch_atomic_long_inc_overflow(v, L) \
> +({ \
> + arch_atomic64_inc_overflow((v), L) \
> +})
> +
> +#define arch_atomic_long_dec_overflow(v, L) \
> +({ \
> + arch_atomic64_dec_overflow((v), L) \
> +})
> +
> +#define arch_atomic_long_dec_and_test_overflow(v, L) \
> +({ \
> + arch_atomic64_dec_and_test_overflow((v), L) \
> +})
> +
> #else /* CONFIG_64BIT */
>
> static __always_inline long
> @@ -1009,6 +1024,21 @@ arch_atomic_long_dec_if_positive(atomic_
> return arch_atomic_dec_if_positive(v);
> }
>
> +#define arch_atomic_long_inc_overflow(v, L) \
> +({ \
> + arch_atomic_inc_overflow((v), L) \
> +})
> +
> +#define arch_atomic_long_dec_overflow(v, L) \
> +({ \
> + arch_atomic_dec_overflow((v), L) \
> +})
> +
> +#define arch_atomic_long_dec_and_test_overflow(v, L) \
> +({ \
> + arch_atomic_dec_and_test_overflow((v), L) \
> +})
> +
> #endif /* CONFIG_64BIT */
> #endif /* _LINUX_ATOMIC_LONG_H */
> -// e8f0e08ff072b74d180eabe2ad001282b38c2c88
> +// 487bc4fea91f23f2a4b42af7d5b49ef9172ae792
> --- a/scripts/atomic/atomics.tbl
> +++ b/scripts/atomic/atomics.tbl
> @@ -44,3 +44,6 @@ inc_not_zero b v
> inc_unless_negative b v
> dec_unless_positive b v
> dec_if_positive i v
> +inc_overflow n v L
> +dec_overflow n v L
> +dec_and_test_overflow m v L
> --- /dev/null
> +++ b/scripts/atomic/fallbacks/dec_and_test_overflow
> @@ -0,0 +1,12 @@
> +cat << EOF
> +#define arch_${atomic}_dec_and_test_overflow(_v, _label) \\
> +({ \\
> + bool __ret = false; \\
> + ${int} __new = arch_${atomic}_dec_return(_v); \\
> + if (unlikely(__new < 0)) \\
> + goto _label; \\
> + if (unlikely(__new == 0)) \\
> + __ret = true; \\
> + __ret; \\
> +})
> +EOF
> --- /dev/null
> +++ b/scripts/atomic/fallbacks/dec_overflow
> @@ -0,0 +1,8 @@
> +cat << EOF
> +#define arch_${atomic}_dec_overflow(_v, _label) \\
> +do { \\
> + ${int} __new = arch_${atomic}_dec_return(_v); \\
> + if (unlikely(__new <= 0)) \\
> + goto _label; \\
> +} while (0)
> +EOF
> --- /dev/null
> +++ b/scripts/atomic/fallbacks/inc_overflow
> @@ -0,0 +1,8 @@
> +cat << EOF
> +#define arch_${atomic}_inc_overflow(_v, _label) \\
> +do { \\
> + ${int} __old = arch_${atomic}_fetch_inc(_v); \\
> + if (unlikely(__old <= 0)) \\
> + goto _label; \\
> +} while (0)
> +EOF
>
>
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